Influence of Photo-induced bond-breaking and bond-formation on phase separation kinetics polymeric fluids: DPD simulation insights*

We study the phase separation dynamics of block copolymer (BCP) melt in d=3 using the dissipative particle dynamics (DPD) simulation method. The system is subjected to external stimuli such as light. A homogeneously mixed BCP melt is rapidly quenched below the critical temperature, and we let the system go through alternate light “on” and “off” cycles. An on-cycle breaks the stimuli-sensitive bonds connecting blocks A and B in BCP melt, and broken bonds reconnect during the off-cycle. The variation in bond breaking rate constant mimics an impression of variation in light intensity. By simulating the effect of light, we isolate scenarios where phase separation begins with the light off (set 1); the cooperative interactions within the system allow it to undergo microphase separation. When the light is on (set 2), the system undergoes macrophase separation due to the bond breaking. Here, we report the role of alternate cycles on domain morphology by varying bond-breaking probability for both sets. We observe that the scaling functions depend upon the conditions mentioned above that change the time scale of the evolving morphologies in various cycles. The average domain size respects the power-law growth: R(t) ~ t^Φ at late times for all the cases, where Φ is the dynamic growth exponent. However, the effect of bond-breaking on the separation kinetics becomes more noticeable up to the system passing through the first light-on cycle.